Changes in Accumulated Other Comprehensive Losses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at January 1	$ (4,859)
Components of Other Comprehensive Income (Loss):
Before Reclassifications	61
Reclassifications	507
Other Comprehensive Gain (Loss), Net of Tax	568	$ (1,280)	$ 2,790
Balance at December 31	(4,291)	(4,859)
Income tax expense	132	11,892	14,308
Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at January 1	(96)
Components of Other Comprehensive Income (Loss):
Before Reclassifications	(44)
Reclassifications	0
Other Comprehensive Gain (Loss), Net of Tax	(44)	(73)	42
Balance at December 31	(140)	(96)
Unrealized Holding Gains (Losses) on Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at January 1	(8)
Components of Other Comprehensive Income (Loss):
Before Reclassifications	(21)
Reclassifications	0
Other Comprehensive Gain (Loss), Net of Tax	(21)	(2)	(7)
Balance at December 31	(29)	(8)
Derivatives [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at January 1	(2)
Components of Other Comprehensive Income (Loss):
Before Reclassifications	0
Reclassifications	0
Other Comprehensive Gain (Loss), Net of Tax	0	(54)	(73)
Balance at December 31	(2)	(2)
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at January 1	(4,753)
Components of Other Comprehensive Income (Loss):
Before Reclassifications	126
Reclassifications	507
Other Comprehensive Gain (Loss), Net of Tax	633	(1,151)	$ 2,828
Balance at December 31	(4,120)	$ (4,753)
Defined Benefit Plans [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Components of Other Comprehensive Income (Loss):
Employee benefits reclassification component, included in employee benefit costs	824
Income tax expense	$ 317